.ag-column-drop-cell {
    box-shadow: 0 0 4px purple;
}
/* The different sections within the columns tool panel use
   flex sizing to adapt to vertical space, use min-height
   and max-height to constrain their heights */
.ag-column-drop-vertical-rowgroup {
    min-height: 120px;
}
.ag-column-drop-vertical-aggregation {
    min-height: 90px;
}
